1. Field of the Invention
This invention relates to an ink-jet recording sheet, more specifically, to an ink-jet recording sheet which causes no crack at the surface of an ink-receptive layer, and excellent in water fastness, light fastness, ink absorption property and glossiness.
2. Prior Art
As a recording sheet to be used for an ink-jet recording, a recording sheet which comprises, on a support such as a usual paper or the so-called ink-jet recording sheet, a porous ink absorption layer containing a pigment such as silica fine particles, and a hydrophilic binder such as polyvinyl alcohol has been known.
There have been proposed recording sheets obtained by coating silica fine particles and a hydrophilic binder onto a paper support as disclosed in, for example, Japanese Provisional Patent Publications No. 51583/1980, No. 157/1981, No. 107879/1982, No.107880/1982, No. 230787/1984, No.160277/1987, No.184879/1987, No. 183382/1987, No. 11877/1989, and the like. These recording sheets are poor in water fastness, image quality and surface gloss since they comprise a combination of a pigment and a binder.
Also, in Japanese Patent Publication No. 56552/1991, Japanese Provisional Patent Publications No. 188287/1990, No. 81064/1998, No. 119423/1998, No. 175365/1998, No. 203006/1998, No. 217601/1998, No.20300/1999, No.20306/1999 and No.24481/1999, there have been disclosed ink-jet recording sheets using synthetic silica fine particles prepared by a gas phase process (hereinafter referred to as xe2x80x9cfumed silicaxe2x80x9d). The fumed silica is ultrafine particles having an average particle size of a primary particle of several nm to several tens nm, and has characteristics of easily giving high gloss.
As a support for the above-mentioned recording sheet, paper has conventionally been used in general and the paper itself had a role as an ink absorption layer. In recent years, a recording sheet having characteristics like photography has earnestly been desired. However, a recording sheet using paper as a support has problems of gloss, the feel of a material, water fastness, cockling (wrinkle or surface waviness) and the like. Thus, a water-resistant support such as a plastic resin film including a polyethylene film, or a polyolefin-coated paper in which a polyolefin resin such as polyethylene is laminated on the both surfaces of paper has now been used. However, these water-resistant supports cannot absorb ink which are differ from a paper support so that it is important that an ink-receptive layer provided on the support has a high ink absorption property. Accordingly, to prepare a recording sheet using a water-resistant support, a much amount of a pigment should be coated on the support as compared with that of a recording sheet using a paper support. When the content of the pigment is increased, surface crack (craze) is likely caused at the time of drying an ink-receptive layer after coating whereby the quality of the sheet is markedly lowered.
Occurrence of surface crack is likely caused when the primary average particle size is much smaller, and it is more likely caused in the fumed silica mentioned above. Also, to obtain high absorption property of ink, it is preferred to decrease a ratio of the content of a hydrophilic binder based on the content of silica fine particles. Thus, if the content of the hydrophilic binder is increased, surface crack is more likely caused.
Also, for the recording sheet, high levels of water fastness and light fastness are required. However, the above-mentioned conventional recording sheets did not sufficiently satisfy these required characteristics. Here, the water fastness means that ink of a recording image is not blurred or dissolved out when the recording sheet after printing is brought into contact with water or allowed to stand under highly humid conditions. The light fastness means that an image does not fade away when the recording sheet after printing is exposed to light.
As a method for improving water fastness, there has been known to use a water-soluble organic cationic polymer for fixing a water-soluble ink, as disclosed in, for example, Japanese Provisional Patent Publications No. 49990/1985, No. 83882/1985, No. 58788/1986, No. 174184/1987, No. 86508/1998, No. 193776/1998, and No. 217601/1998. However, there are problems that most of these water-soluble organic cationic polymers which improve the water fastness are always to make the light fastness worsen, while those which do not affect on the light fastness are always insufficient in water fastness. It is the present status that a water-soluble organic cationic polymer which can satisfy both of the water fastness and light fastness cannot be obtained as of today. Moreover, there is a problem that these water-soluble organic cationic polymers cause aggregation of silica fine particles easily when they are mixed with these silica fine particles so that coating property becomes worse and occurrence of surface crack or lowering in gloss are caused.
Also, as the other method for improving water fastness, it has been proposed to use polyaluminum hydroxychloride in, for example, Japanese Provisional Patent Publications No. 257286/1985, No. 16884/1986, etc., to use zirconium in Japanese Provisional Patent Publication No. 32046/1994, or to use an element of Group 4 of the Periodic Table in Japanese Provisional Patent Publications No.258567/1998, No. 309862/1998, etc. By using these compounds, a certain extent of an improvement has been admitted in water fastness, but the above-mentioned ink-jet recording sheets are not satisfied in gloss and ink absorption property.
Also, in a recording sheet using silica fine particles having a primary average particle size of 20 nm or less, there is a problem that the recording sheet is warped at the time of handling, crack is likely caused at the surface thereof so that improvement has been desired.
In a recording sheet which is an object of the present invention, there is a problem that a recorded image is likely fade away by a minute amount of gases which cause bad effects such as ozone, etc. existing in air when it is exposed to air. In particular, ultrafine particulate silica having a primary average particle size of 20 nm or less has a large specific surface area so that a surface area which is in contact with air becomes large whereby it is likely damaged by a minute amount of gas. Moreover, as mentioned above, by decreasing an amount of a hydrophilic binder to heighten ink absorption property, the silica is suffered from a bad effect caused by a minute amount of gas. Thus, it has also earnestly been desired to overcome this problem.
An object of the present invention is to provide an ink-jet recording sheet which has no surface defect such as surface cracking, etc., and has high gloss, excellent water fastness, light fastness and ink absorption property simultaneously. Another object of the present invention is to provide an ink-jet recording sheet which causes no surface crack at the time of operation. Still another object of the present invention is to provide an ink-jet recording sheet which can prevent from fading due to a minute amount of gas in air.
The above objects of the present invention have been achieved by an ink-jet recording sheet which comprises a support and at least one ink-receptive layer provided on the support, wherein at least one of the ink-receptive layer contains silica fine particles having an average primary particle diameter of 20 nm or less and at least one water-soluble polyvalent metal compound.